Mapping antioxidant mechanisms in plant extracts via reactivity kinetics inhibiting oil autoxidation

This study aims to investigate the reactivity kinetics of natural antioxidants in plant extracts from three families (Asteraceae, Lamiaceae, and Rosaceae) in inhibiting sunflower oil autoxidation. Extracts obtained via ultrasound-assisted extraction were added to stripped sunflower oil (SSO; natural antioxidants removed) and autoxidation kinetics were monitored using isothermal calorimetry at 30 °C. Of the 15 tested extracts, 11 efficiently inhibited SSO autoxidation, with inhibition rate constants (kinh) on the order of 104 M-1s-1. Satureja montana and Tagetes erecta exhibited the highest kinh values. To better understand antioxidant mechanisms, extracts were characterized for their phytochemical composition, and the major phenolic compounds identified were tested individually. Rosmarinic acid showed the highest kinh value, followed by quercetin ≈ caffeic acid > catechin > chlorogenic acid > ellagic acid > luteolin. The kinh values of the whole extracts were lower than those of the most reactive individual compounds, suggesting competitive interactions among constituents with varying reactivities that diminish overall antioxidant performance. Lamiaceae species, rich in rosmarinic acid, were particularly effective at scavenging peroxyl radicals and demonstrated strong potential as natural alternatives to synthetic antioxidant, BHT. By linking phytochemical composition with kinetic behavior, this study offers mechanistic insights into how antioxidants function in complex systems. The findings support the use of plant-based antioxidants in food preservation and propose a robust, kinetics-based approach for evaluating antioxidant performance in complex mixtures.